1. Field of the Invention
The present invention relates to molecular scale mechanical devices.
2. Description of the Related Art
Recent reports of molecular scale devices include systems based on catenanes and rotaxanes (Pease et al., 2001 Jimenez et al., Brouwer et al., 2001), chiroptical molecular switches (Koumera et al., 1999), molecular ratchets (Kelly et al., 1999) and DNA (Mao et al., 1999). These devices are activated by triggers, i.e., redox, small molecule or ionic effectors, light or temperature, that act equally on all devices present.
DNA nanotechnology entails the construction of objects, arrays and devices that utilize unusual motifs. The laboratory of the present inventors reported the first DNA-based nanomechanical device, based on the B-Z (right-hand to left-hand) transition of DNA (Mao et al. 1999). The B to Z transition is activated/deactivated by the presence or absence of high ionic strength or by small molecule effectors, such as (Co(NH3)6Cl3, that facilitate it. This first prototype DNA nanomechanical device consisted of two double crossover molecules of DNA attached to a piece of DNA that could switch from B- to Z-DNA, thereby changing the rotational position of one of the double crossovers by about a half turn, which resulted in atoms moving by 20-60 Angstroms, depending on their distance from the rotation axis. The device was actuated by the addition of a chemical actuator, Co(NH3)6+++, to the solution, and returned to its original conformation when the Co(NH3)6+++ was removed.
Assembly of DNA arrays with patterns produced by a variety of components localized according to programmed self-assembly were reported by the laboratory of the present inventors (Winfree et al., 1998; Liu et al., 1999; Mao et al., 1999; LaBean et al., 2000; Sha et al., 2000; Mao et al., 2000). The incorporation of molecular devices into arrays could lead to the complex structural states necessary for nanorobotics, but the activators would need to be localized very tightly to address individual devices. Were N such devices to be incorporated into a 2D or 3D array, there would only be two states, that corresponding to B-DNA and that corresponding to Z-DNA, except perhaps for a small amount of nuance.
It is desirable to be able to produce more structural states within an array, ideally at least 2N states, by, i.e., producing a variety of 2-state devices that can be individually programmed, rather than programmed by the addition of the same chemical. A mechanism to effect this type of control with DNA has been prototyped recently but the system to which it was applied generates by-products and is therefore not robust (Yurke et al., 2000). The Yurke et al. device operates by the addition of a DNA strand of a specific sequence to a partial motif. When doing so, Yurke et al. obtained a population of about 80% monomers of their target complex and 20% dimers. Thus, the products in the Yurke et al. device are only partially stable and partially predictable, i.e., not robust.
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